12 volts at battery when boat is off and also when idling. replace alternator?

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danfinn

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Took the boat out on the lake this weekend after it had sat for about 6 weeks. It started up fine, it was maybe a little sluggish cranking over. Got it out on the lake and ran fine. Stopped for a bit and it seemed to have trouble starting back up. Got it running and back on the trailer and home.

I connected my volt meter to the batter. I had 12 volts with the boat off. Started the boat up and with it idling I still had 12 volts. I believe I should be closer to 14 volts at the battery with the boat running, is that correct? Is this a sign that the alternator needs to be replaced? Before I do that, is there anything else I can test to be sure that is what should be replaced?
 
Don S

Don S

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Re: 12 volts at battery when boat is off and also when idling. replace alternator?

You may have to speed the engine up 1500 rpm to get the alternator to start charging. Then check the voltage at that rpm.

What are we working on?
 
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danfinn

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Re: 12 volts at battery when boat is off and also when idling. replace alternator?

Don S said:
You may have to speed the engine up 1500 rpm to get the alternator to start charging. Then check the voltage at that rpm.

What are we working on?
Click to expand...

1994 Montery with a Mercruiser 4.3 LX

I'll try it again at higher RPM
 
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danfinn

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Re: 12 volts at battery when boat is off and also when idling. replace alternator?

Battery read 13.9 with the boat at 1500 RPM so maybe it's not the alternator/battery. Maybe the starter? It did click a couple of times this last time when starting it cold and then it finally turned over. That's what it was doing out on the lake as well.
 
Don S

Don S

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Re: 12 volts at battery when boat is off and also when idling. replace alternator?

Could also be a failing battery. Sure wouldn't be the first.
Have it load tested, not just checked for voltage.

May also be bad connections. Clean tight battery cable connections are a must.
When you ran at 1500 rpm, did you have 13.9 showing at the battery as well?
 
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Glaspar_Fan

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Re: 12 volts at battery when boat is off and also when idling. replace alternator?

And clean up the cables at the battery terminals, the negative to engine connection and the positive to starter connection.
 
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fishrdan

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Re: 12 volts at battery when boat is off and also when idling. replace alternator?

danfinn said:
Battery read 13.9 with the boat at 1500 RPM
Click to expand...

Did the battery continue to read 13.9 volts (or something close) when dropped back to idle? The Alternator won't start charging until it reaches it's cut-in RPM, but it should continue to keep charging when dropped back to idle.
 
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dingdongs

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Re: 12 volts at battery when boat is off and also when idling. replace alternator?

the battery needs to be of good quality and if its more than 5 years old may be on its last legs.if all terminals are proved to be clean and the voltage should be high 12's at rest.
they require all the available amps for the starting process so if all is well on that front a solenoid may be causing the clicking you are hearing and its a relativly cheap replacement to get the boat reliable again.
 
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danfinn

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Re: 12 volts at battery when boat is off and also when idling. replace alternator?

fishrdan said:
Did the battery continue to read 13.9 volts (or something close) when dropped back to idle? The Alternator won't start charging until it reaches it's cut-in RPM, but it should continue to keep charging when dropped back to idle.
Click to expand...

Guess I need to go out and test it again, didn't check for that.
 
Don S

Don S

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Re: 12 volts at battery when boat is off and also when idling. replace alternator?

Did you look at the service bulletin I posted earlier? It details all the tests you need to do to find out what is wrong.

print it out and go follow the instructions.
 
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